The following relates to the optoelectronic arts. It especially relates to light emitting diode-based assemblies and methods for making same. However, the following will also find application in conjunction with other optoelectronic device assemblies, such as photodetector assemblies, laser diode assemblies, solar cell assemblies, and so forth, and in methods for making same.
Light emitting diode assemblies are of interest for lighting, display, lighted signage, and other applications. A typical light emitting diode assembly includes one or more light emitting diode packages mounted on a circuit board that serves as a mechanical substrate and provides electrical connection between the light emitting diode package or packages and an electrical power path or input.
Some light emitting diode assemblies are used in applications, such as outdoor applications, automotive applications, or so forth, that expose the assembly to weathering or other environmental hazards. In outdoor applications, for example, exposure to rain, snow, humidity, or the like can produce water-related damage to the light emitting diode assembly.
One known approach to protecting light emitting diode assemblies from such environmental hazards is to provide an outer waterproof container or housing. For maximum light output, the housing should include openings through which the light emitting diodes emit light. However, it is difficult to make an adequately waterproofed housing. Incorporating a waterproof housing also increases the cost and complexity of the light emitting diode assembly.
Overmolding, potting, or other sealing approaches are also known. Indeed, it is well known to pot electronics for the purpose of protecting the electronics from environmental hazards. However, a difficulty arises in the case of a light emitting diode assembly, in that light emission from the overmolded, potted, or otherwise sealed assembly should not be inhibited.
One option is to use a light-transmissive sealant. However, this limits the selection of sealant materials. Additionally, some light absorption or light scattering can be expected even in a nominally light-transmissive sealant.
Another approach is to avoid sealing the light emitting diode packages. In a typical approach, the tooling mold includes generally hollow members, sometimes called pins, that isolate the light emitting diode package from the injected sealant material during injection overmolding.
A sealant that does not cover the light emitting diode packages advantageously reduces exposure-related degradation and failures of light emitting diode assemblies, while providing unimpeded light output. However, some exposure-related assembly degradation and occasional failures are still observed. Even a relatively low failure rate is problematic for some type of light emitting diode assemblies. For example, failure of outdoor illuminated signage can result in lost advertising or adverse advertising in the form of an unsightly unlit sign. Failure of automotive lighting assemblies may manifest as a “broken taillight” or other inoperative vehicle light. Failure of a traffic light, crosswalk light, railway light, or other directional signage can confuse travelers and reduce traffic flow efficiency.
An intermediate option is to use a light-transmissive sealant applied as part of a two-shot overmolding process. For example, in a first shot a thin transparent sealant is disposed over the light emitting diode packages, and in a second shot the bulk of the overmolding is applied. Advantageously, this approach allows the molding material and thickness of each step to be selected for its specific purpose. By using a thin first-shot overmolding of a highly transparent material light absorption, scattering, or so forth is reduced. The second shot can then apply a thick overmolding of a material that need not have any special optical characteristics, and indeed can be completely opaque to light generated by the light emitting diode packages.
However, two-shot overmolding is problematic from a manufacturing standpoint. The cost of two-shot overmolding is substantially higher than the cost of single-shot overmolding. Moreover, two-shot overmolding employs more complex machinery including mechanisms to change the geometry of filling cavities, the use of two different injectors, and so forth. The additional complexity can adversely affect factory up-time, device yield, and other manufacturing productivity metrics.
The following contemplates improved assemblies and methods that overcome the above-mentioned limitations and others.